Enantioselective Optical Trapping of Chiral Nanoparticles with Plasmonic Tweezers

Enantiomer separation is a critical step in many chemical syntheses, particularly for pharmaceuticals, but prevailing chemical methods remain inefficient. Here, we introduce an optical technique to sort chiral specimens using coaxial plasmonic apertures. These apertures are composed of a deeply subwavelength silica channel embedded in silver and can stably trap sub-20 nm dielectric nanoparticles. Using both full-field simulations and analytic calculations, we show that selective trapping of enantiomers can be achieved with circularly polarized illumination. Opposite enantiomers experience distinct trapping forces in both sign and magnitude: one is trapped in a deep potential well, while the other is repelled with a potential barrier. These potentials maintain opposite signs across a range of chiral polarizabilities and enantiomer-aperture separations. Our theory indicates that the interaction of chiral light and chiral specimens can be mediated by achiral plasmonic apertures, providing a possible route toward all-optical enantiopure syntheses.